Short Take Off and Vertical Landing (STOVL) aircraft and Vertical Take Off and Landing (VTOL) aircraft are known to generate intense noise and unsteady pressure fluctuations during landing and takeoff operations. The most severe environment is when such an aircraft is within about 10 feet of an aircraft carrier deck, the ground, or a launch/landing pad. The noise and pressure fluctuations at these operating conditions are usually about 10 dB higher than that of free flight. Pressure fluctuations can also be resonant with the aircraft structure, inducing acoustic fatigue.
To prevent structural failure due to acoustic fatigue, a STOVL aircraft must carry extra weight to reinforce its structure. Some analysts suggest that as much as 100 pounds of extra structural weight can be eliminated if the noise levels at landing and takeoff can be reduced by about 3 to 5 dB.
Clearly, the reduction of the noise/pressure fluctuations for STOVL operations is an important environmental issue, in addition to the impact on aircraft design and cost. Many techniques have been utilized in the past to reduce the impact of high velocity exhaust flow, but these techniques almost exclusively focus on the aircraft itself. This inevitably adds implementation cost and extra weight to the aircraft. There is a need to minimize the magnitude of the noise and unsteady pressure fluctuations of the exhaust flow rather than merely minimizing the destructive results thereof. The present invention is directed to solving one or more problems associated with the prior art.